Only the latest version of the game is fully supported as it contains all the latest improvements, fixes and changes. If you encountered any issues on an older version of the game, make sure to update it first.
However, if for any reason you wish to revert to an earlier version of the game, here's how you can do it:
Steam
1. Go to your Steam Library.
2. Right-click on The Witcher 3: Wild Hunt and select Properties.
3. Go to BETAS and select CLASSIC - the game will update automatically.
To return to the newest version of the game, simply follow the same steps and select "None" in the BETAS menu.
GOG
1. Go to your “Installed” section on GOG Galaxy.
2. Select The Witcher 3: Wild Hunt and select Manage Installation → Configure…
3. Change Beta Channels to Classic.
4. Disable the auto-updates option, choose your preferred version, and click OK.
To return to the newest version of the game, simply follow the same steps and select "Disabled" in the Beta Channels menu.